After turning off hot and/or cold water faucets (or after flushing toilet) in my bathroom, I hear a banging (hammer-like affect) sound from my water pipes behind the walls of the bathroom. I live in a Condo that has no cellar but sits on a concrete foundation pad. This issue occurs in both bathrooms, up stairs and down. What causes this? And, what can I do to eliminate this situation!

You used the right term to describe the noise, it is actually called a water hammer, it is caused when you turn the water off sudenly and the water has to stop instantly, and since water will not compress it is like a steel rod hitting the end of the pipe.

To stop this you have to install an air chamber. This is a column of air in a pipe connected to you water pipes. As the water is turned off it compresses the air in the air chamber and therefore dampens the noise made by the water hammer.

Some houses do not have this problem at all others have a lot. It is possible that you might have to install more than one, and at different places in the home. One could be installed at the water inlet of the water heater, others could be installed under the sinks in the supply lines. I would put one on the hot and the cold supplies.

You can make these by soldering a cap on the end of a piece of 3/4 copper about 6 inches long and a adapter on the other end that you can tie into the supply lines. The one at the water heater I would make of 1-1/2 inch copper pipe and a cap on one end and a 1-1/2 X3/4 inch reducer on the other so you can tie into the water line at the water heater.

Please let me know if this answer helped you.

How old is your condo and what state are you in. Its been standard procedure to set all fixtuire with an air chamber iniside the wall for the past 25 years. Your chambers may have filled over the years as the air slowly gets absorbed by the water, Try shutting off you main, drain the entire home and then open the connection of the supply pipe to the stop below your sinks and toilet. This will let air chamber water to drain and refill it with air. If this fails you can install the chamber Letmetellu has described.

Thanks Letmetellu:
I'll talk with my local plumber re: this. At least now I can talk intelligently to him about the plumbing problem

Ballenger1:

Condo is 22 years old and is located on Cape Cod in Massachusetts

You should have air chambers already built in but call your local building inspector to confirm what they enforced 22 years ago. To answer Letmetellu's question, I do at time need to tap the cambers on the side with a screw driver to just to break loose the vacuum caused by the water trapped in such a small pipe.